System and method for hybrid refrigeration gas liquefaction

ABSTRACT

In an embodiment, a method includes cooling a fluid along a fluid path using a vapor compression refrigeration cycle; cooling the fluid along the fluid path using at least one cryocooler of a cryogenic cooling phase; expanding the fluid during cooling within the cryogenic cooling phase, after cooling in the cryogenic cooling phase, or a combination thereof, such that a temperature and pressure of the fluid are reduced to generate a fluid stream having both a vapor phase and a liquid phase; and condensing the vapor phase. The fluid may be a natural gas.

BACKGROUND

Natural gas, when isolated from natural sources (e.g., underground in naturally occurring reservoirs), generally includes a mixture of hydrocarbons. The major constituent in these hydrocarbons is methane, which is generally referred to as natural gas in commerce. Natural gas is useful as a source of energy because, among other things, it is highly combustible. One particularly desirable characteristic of natural gas is that it is generally considered to be the cleanest hydrocarbon for combustion. Because of this, natural gas is often used as fuel in a wide variety of settings, including heaters in residential homes, gas stoves and ovens, dryers, water heaters, incinerators, glass melting systems, food processing plants, industrial boilers, among numerous others. Generally, natural gas (e.g., untreated or raw natural gas) removed from reservoirs is processed and cleaned prior to entering pipelines that eventually feed the gas to homes and industrial plants. For example, natural gas may be processed to remove oil and condensates, water, sulfur, and carbon dioxide. During these processes, natural gas may be liquefied, which may facilitate separation (e.g., purification) and transport.

Natural gas may be transferred to various destinations via pipelines or, in certain situations, via storage vessels. Unfortunately, pipeline networks can represent a significant investment, and are generally used only in situations where the natural gas is traveling a relatively short distance. When natural gas is extracted far from its final destination, transportation by way of storage vessels may be more economical. Indeed, as oil and coal resources become scarcer, the demand for liquefied natural gas has increased significantly because of its ability to be transported to destinations that do not have access to a pipeline.

In these situations, the natural gas may be liquefied, transported in a vessel that will keep the gas at cryogenic temperatures, and re-vaporized upon arrival at its destination. Natural gas condenses to its liquid state at about −260° F., or approximately −162° C. Accordingly, it should be appreciated that reaching such a low temperature on a large scale, while also maintaining these temperatures during transport, can be challenging. For example, traditional refrigeration techniques may be sufficient to reach or maintain these temperatures. However, these techniques can often involve significant capital investment, such as in refrigerant, compressors, and so forth. Therefore, typical approaches to liquefying natural gas may be subject to further improvement.

BRIEF DESCRIPTION

Certain embodiments commensurate in scope with the originally claimed subject matter are summarized below. These embodiments are not intended to limit the scope of the claimed subject matter, but rather these embodiments are intended only to provide a brief summary of possible embodiments. Indeed, the present disclosure may encompass a variety of forms that may be similar to or different from the embodiments set forth below.

In one embodiment, a gas feed liquefaction system includes a flow path; an initial cooling phase in a first heat exchange relationship with the flow path, wherein the initial cooling phase includes a vapor compression refrigeration cycle; a second cooling phase in a second heat exchange relationship with the flow path, wherein the second cooling phase includes a first cryocooler in series with the initial cooling phase; and a first expander positioned along the flow path between the first cryocooler and a separation vessel having a first liquid outlet and a vapor outlet.

In another embodiment, a system includes a natural gas flow path; a vapor compression refrigeration cycle configured to remove heat from the natural gas flow path; a first cryogenic cooling phase comprising at least two cryocoolers configured to remove heat from the natural gas flow path; a driver configured to drive the at least two cryocoolers, wherein the at least two cryocoolers are connected by a common buffer tube; and a liquefied natural gas outlet path downstream from the vapor compression refrigeration cycle and the cryogenic cooling phase.

In a further embodiment, a method includes cooling a fluid along a fluid path using a vapor compression refrigeration cycle; cooling the fluid along the fluid path using at least one cryocooler of a cryogenic cooling phase; expanding the fluid during cooling within the cryogenic cooling phase, after cooling in the cryogenic cooling phase, or a combination thereof, such that a temperature and pressure of the fluid are reduced to generate a fluid stream having both a vapor phase and a liquid phase; and condensing the vapor phase.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIG. 1 is a block diagram of an embodiment for the overall process of making and utilizing a liquefied gas, in accordance with an aspect of the present disclosure;

FIG. 2 is a process flow diagram of an embodiment of a hybrid refrigeration gas liquefaction system that includes a vapor compression refrigeration cycle, first and second cryogenic cooling phases, and one or more expansion apparatus that all operate to cool and condense a natural gas stream, in accordance with an aspect of the present disclosure;

FIG. 3 is a process flow diagram of an embodiment of the hybrid refrigeration gas liquefaction system of FIG. 2, where the first cryogenic cooling phase includes multiple cryocoolers and expansion apparatus, and where the first and second cryogenic cooling phases are heat-integrated with the vapor compression refrigeration cycle, in accordance with an aspect of the present disclosure;

FIG. 4 is a process flow diagram of an embodiment of the hybrid refrigeration gas liquefaction system of FIG. 2 having a control system that contors operation of various cooling, flow, and compression components based on feedback received from one or more sensors positioned throughout the system, in accordance with an aspect of the present disclosure;

FIG. 5 is a process flow diagram of an embodiment of the hybrid refrigeration gas liquefaction system of FIG. 2 having a plurality of intermediate flow paths each having at least two cryocoolers in series that are driven using a single driver, in accordance with an aspect of the present disclosure;

FIG. 6 is a process flow diagram of an embodiment of the hybrid refrigeration gas liquefaction system of FIG. 2 having a plurality of intermediate flow paths each having at least two cryocoolers in series, and where at least two cryocoolers arranged parallel to one another are driven using a single driver, in accordance with an aspect of the present disclosure;

FIG. 7 is a block diagram of an embodiment of a hybrid refrigeration gas liquefaction method, in accordance with an aspect of the present disclosure;

FIG. 8 is a block diagram of an embodiment of a hybrid refrigeration gas liquefaction method in which the subject gas is used for refrigeration, in accordance with an aspect of the present disclosure; and

FIG. 9 is a process flow diagram of an embodiment of the hybrid gas liquefaction system of FIG. 2, in accordance with an aspect of the present disclosure.

DETAILED DESCRIPTION

One or more specific embodiments will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Furthermore, any numerical examples in the following discussion are intended to be non-limiting, and thus additional numerical values, ranges, and percentages are within the scope of the disclosed embodiments.

Natural gas (NG) liquefaction plants may utilize a vapor compression refrigeration process to cool natural gas to its liquid state. These processes may include one or more compressors to compress a refrigerant, which may then be condensed (e.g., using a cooling medium such as water) and cooled by flash evaporation. This cooled refrigerant may be used to cool the natural gas by way of heat exchange. Because the cooled refrigerant may not, in a single heat exchange, be sufficient to condense the natural gas to its liquid state, multiple heat exchanges using multiple vapor compression refrigeration cycles may be used to reach a liquefaction temperature of the natural gas.

In accordance with present embodiments, one or more vapor compression refrigeration cycles may be used in combination with one or more other cooling cycles, such as cryocooling cycles (e.g., thermoacoustic cryocooling, mechanically-driven cryocooling) in order to achieve such temperatures. Further, it is now recognized that the integration of these cooling methods may be further enhanced by the modification of the cryocooling stages (e.g., one or more of the cryocooler stages) to include additional processes that enable more efficient cooling.

Thermoacoustic cryocoolers utilize the principle that compressed fluids are more readily able to transfer energy whereas expanded fluids absorb energy at a faster rate. Thermoacoustic cryocoolers include a working fluid that is subjected to pressure and velocity fluctuations, which causes the working fluid to form a resonant wave and create a temperature gradient through a high heat capacity material called the “stack” or “regenerator.” The regenerator includes a higher temperature heat exchanger on one end and a lower temperature heat exchanger on the opposite end. Thermoacoustic cryocoolers can reach lower temperatures than vapor compression refrigeration systems and also contain fewer moving parts. However, they are generally relatively small compared to vapor compression refrigeration cycles, and their throughput is, as a result, also relatively smaller. As an example, vapor compression refrigeration cycles for natural gas implementations are generally between approximately 5 and 10 times larger and have about the same level of increased throughput compared to thermoacoustic cryocoolers. Accordingly, the size of the cryocoolers may be prohibitive when considering the throughput desired for natural gas liquefaction in industrial applications. The present disclosure includes embodiments in which these refrigeration methods may be utilized in conjunction with one another on a relatively large scale, despite the relatively low throughput of cryocoolers compared to vapor compression refrigeration cycles.

Thermoacoustic cryocoolers operate at the highest efficiency when the material being cooled is at relatively low temperatures. This may be due, at least in part, to the restricted thermal contact time between the working fluid with the fluid (e.g., natural gas) stream. In some embodiments, maximum energy transfer (e.g., maximum cooling of the fluid stream) can occur when the fluid stream is at a relatively low temperature.

As discussed herein, in embodiments where more than one cryocooling stages (e.g., more than one cryocooler) are employed, one or more expansion valves (e.g., a Joule-Thomson (JT) valve) may be utilized between the cryocooling stages in order to achieve increased cooling efficiency by the cryocoolers. Thus, the expansion valves may be positioned along a refrigeration path of the natural gas (i.e., a path along which the natural gas flows to be refrigerated) such that as the natural gas passes through each expansion valve, at least a portion of the natural gas flash evaporates. Due to this adiabatic expansion, the natural gas is cooled.

While the expansion of natural gas in this manner may seem to be counterproductive when the desired result is a liquefied natural gas, an increase in the efficiency of each cryocooler may be achieved when such flash evaporation is performed. In other words, the effect of each cryocooler on the natural gas may be enhanced by adiabatically expanding the natural gas before the natural gas is cooled by the cryocooling stages. This may be due, at least in part, to the adiabatic expansion enabling the natural gas to reach a temperature that is closer to the temperature of a desired (e.g., optimum or design) fluid operating temperature of the cryocooler(s). Advantages achieved by such expansion include, but are not limited to, the use of a fewer number of cooling stages and a decrease in energy requirements needed to operate each cryocooler. Furthermore, the adiabatic expansion may also enable enhanced heat transfer coefficients between the natural gas and the cryocooler, which may be due at least in part to the increased dispersion of the natural gas along the refrigeration path.

In addition to, or in lieu of the approaches above, the present disclosure also includes embodiments in which two or more cryocoolers are driven by a common drive. For example, the two or more cryocoolers may be positioned in series, or in parallel, and may be driven by the same drive. In such a configuration, parasitic losses incurred from the first cryocooler stage (or first set of cryocooler stages) may be used to drive subsequent cryocooler stages (e.g., a second cryocooler stage or second set of cryocooler stages). In some embodiments, one, more than one, or all of the cryocoolers may be thermoacoustic cryocoolers.

As set forth above, in certain embodiments, one or more vapor compression refrigeration cycles may be integrated with one or more cryocooler cooling stages in order to liquefy natural gas on a large scale (e.g., for provision to a natural gas provider for residential and/or commercial use). Turning to the figures, FIG. 1 depicts a process flow diagram of an embodiment of an overall process 10, which includes a number of stages to isolate and use liquefied natural gas.

The process 10 includes an extraction stage 12, where natural gas is extracted from underground reservoirs using, as an example, drilling techniques, fracturing, and so forth. The extracted natural gas may be stored above ground, and/or may be provided (e.g., via a pipeline) to a gasification and processing stage 14. By way of example, in the gasification and processing stage, the natural gas may enter a processing plant to remove certain substances, such as water, carbon dioxide, and sulfur. Removal of these components may enable the gas to burn more efficiently and cleanly.

After the natural gas undergoes the gasification and/or processing stage 14, or simultaneously during this stage, the natural gas may undergo a liquefaction stage 16. In the liquefaction stage 16, the natural gas may be cooled to a temperature of −155° C., where it condenses to a liquid state. In accordance with present embodiments, the natural gas may be cooled by a system including both vapor compression refrigeration and thermoacoustic cryocooling. In some embodiments, this may include a combination of adiabatic expansion of the natural gas followed by cooling using one or more thermoacoustic cryocoolers. Example embodiments of such systems are described in further detail below.

Because of its decreased volume and relatively high cost associated with pipeline transport, the liquid natural gas may be more desirable to transport compared to gaseous natural gas. Accordingly, in some embodiments, the liquid natural gas may undergo a transport stage 18, which may include transporting the liquid natural gas to customers in transportation vessels that keep the liquefied natural gas at the cryogenic temperatures necessary for the liquefied natural gas to remain in a liquid state. Finally, upon reaching its destination, the liquefied natural gas may undergo a re-vaporization stage 19, where the natural gas is converted back into a gaseous state. In its gaseous state, the natural gas may be used as an energy source.

Again, the liquefaction stage 16 may be performed by a system having both a vapor compression refrigeration cycle and at least one thermoacoustic cryocooling stage. FIG. 2 depicts a high-level schematic diagram of one embodiment of such a hybrid refrigeration liquefaction system 20. In the system 20, a flow path 22 carries natural gas 24 through a series of cooling phases to effect liquefaction. The flow path 22 may include one or more conduits or similar features capable of flowing the natural gas 24 in its gaseous and/or liquid state. In certain embodiments, the flow path 22 enters into a heat exchange relationship with multiple cooling phases to cool the natural gas 24. In the illustrated embodiment, a vapor compression refrigeration cycle 26 is present to initially cool the natural gas 24.

It should be noted that while the embodiments discussed herein are presented in the context of the liquefaction of natural gas, other fluids subject to cooling and liquefaction are also presently contemplated. Indeed, the present approaches may be applicable to any liquefaction process performed on any subject fluid, provided that appropriate selections of operating temperatures, pressures, refrigerants, and so forth, are made.

In the illustrated embodiment, the flow path 22 and a refrigerant loop 28 both flow through a heat exchanger 30, which is intended to represent one or more indirect heat exchangers configured to enable the transfer of thermal energy between the natural gas 24 in the flow path 22 and a refrigerant 32 in the refrigerant loop 26. The heat exchanger 30 may be any suitable heat exchanger capable of enabling the transfer of thermal energy between conduits, such as a shell and tube heat exchanger, plate heat exchanger, plate and shell heat exchanger, adiabatic wheel heat exchanger, plate fin heat exchanger, pillow plate heat exchanger, fluid heat exchanger, and the like.

The illustrated vapor compression refrigeration cycle 26 includes vapor compression, cooling, and expansion equipment 34, which may include one or more compressors, one or more heat exchangers, one or more expanders, and so forth. The vapor compression equipment 34 is generally configured to compress the refrigerant 32, cool (e.g., condense) the refrigerant 32, and enable the refrigerant 32 to adiabatically expand and further cool within the refrigerant loop 28. It should be understood that the vapor compression refrigeration cycle 26 may be a part of a vapor compression refrigeration cycle cooling phase, and is intended to represent one or multiple vapor compression refrigeration cycles that each undergo a separate heat exchange with the flow path 22. The various cycles may or may not utilize different substances as the refrigerant 32. By way of non-limiting example, one cycle may utilize propane as the refrigerant 32 while a second cycle may use ethylene as the refrigerant 32.

In one embodiment, the vapor compression refrigeration cooling cycle 26 includes only one refrigerant that undergoes compression and expansion for use as a refrigerant. The only one refrigerant may be propane, and may be substantially free of other refrigerants. As defined herein, the phrase “substantially free of other refrigerants” is intended to denote that if the propane (or other refrigerant used) has any other refrigerants associated with it, the other refrigerants would be present in amounts that are no more than would be expected as impurities.

The flow path 22 exits the heat exchanger 30 (after cooling via the vapor compression refrigeration cycle 24) and enters into a cryogenic cooling phase 36 having at least one thermoacoustic cryocooler 38. In accordance with an embodiment, one or more expansion apparatuses 40 may be present upstream of and/or within the cryogenic cooling phase 36. For example, one or more Joule-Thomson valves may be positioned along the flow path 22 between the heat exchanger 30 and the thermoacoustic cryocooler 38. The expansion apparatus 40 causes the natural gas 42 to undergo adiabatic expansion. As discussed above, while the adiabatic expansion causes a significant decrease in pressure and a concomitant increase in the amount of natural gas vapor, the temperature of the natural gas 24 may also be significantly reduced. This temperature reduction enhances the cooling efficiency of the cryocoolers, as noted above.

The expansion apparatuses 40 may be positioned upstream of the entire first cryocooling phase 36 along the flow path 22, along a divergent flow path leading to a portion of the first cryocooling phase 36, upstream and between one or more of the cryocoolers of the first cryocooling phase 36, downstream of one or more of the cryocoolers of the first cryogenic phase 36, or any combination thereof. Again, such adiabatic expansion may result in a significant increase in cooling efficiency, especially with respect to the cryocoolers.

The cryogenic cooling phase 36 may include only one thermoacoustic cryocooler 38, or multiple thermoacoustic cryocoolers in series or in parallel. In embodiments where multiple thermoacoustic cryocoolers are present, they may be driven with one or more drivers. Indeed, present embodiments provide for two or more of the cryocoolers to be driven using only one driver. Such embodiments are discussed in further detail below.

As noted above, the vapor compression refrigeration cycle 26 is upstream from the cryogenic cooling phase 36. Indeed, because vapor compression refrigeration may be more efficient at cooling gaseous substances when the substance is at a warmer temperature, it may be desirable for the natural gas 24 to be cooled by the vapor compression refrigeration cycle 26 before being cooled by the cryogenic cooling phase 36. However, the present disclosure is also intended to encompass embodiments where all or a part of the cryogenic cooling phase 36 is positioned upstream of the vapor compression refrigeration cycle 26.

In the depicted embodiment, the cryogenic cooling phase 36 may cool the flow path 22 such that a substantial portion (e.g., between approximately 50% and 100%, such as between approximately 60% and 100%, or between approximately 75% and 100%) of the natural gas 24 flowing therethrough condenses into a liquid. Accordingly, upon exiting the cryogenic cooling phase 36, all or a significant portion of the natural gas 24 may be in a liquid state. Upon cooling in the cryocooler phase 36, the natural gas 24 may be provided to a liquid natural gas isolation system 42. In a general sense, the liquid natural gas isolation system 42 is configured to separate liquid and gaseous portions of the natural gas 24 within the flow path 22, and liquefy the remaining gaseous portion.

In the illustrated embodiment, the liquid natural gas isolation system 42 utilizes a second cryogenic cooling phase 44 having at least one cryocooler 46 (e.g., one or more thermoacoustic cryocoolers) and a separator 48. The second cryocooling phase 44 and the separator 48 may be all or only a portion of the liquid natural gas isolation system 42. For example, the liquid natural gas isolation system 42 may also include various expanders, heat exchangers, pumps, and so forth.

The flow path 22 may, as illustrated, fluidly couple an outlet 50 of the first cryocooling phase 36 with an inlet 52 of the separator 48. Generally, in the separator 48, the natural gas 24, which may include both a liquid and vapor phase, may be separated into its constituent fluids. Specifically, the natural gas 24 may be separated in the separator 48 into a first liquid stream 56, which exits the separator 48 at a liquid outlet 58 (e.g., proximate a lower portion or bottom of the separator 48), and a vapor stream 60, which exits the separator 48 at a gas outlet 62 (e.g., proximate an upper portion or top of the separator 48). The separator 48 may, therefore, be kept at a pressure that is appropriate for such separation. Specific examples of pressures are discussed in further detail below with reference to particular embodiments.

Subsequent to phase separation within the separator 48, the vapor stream 60 then enters the second cryocooling phase 44. The second cryocooling phase 44 may include the one or more thermoacoustic cryocoolers 46, which may be used to condense the vapor stream 60 to generate a second liquid stream 64. The second cryocooling phase 44 may also include one or more expansion apparatuses (e.g., Joule-Thompson valves) to enable more efficient cooling and liquefaction of the vapor stream 60. The first and second liquid streams 56, 64 may be combined downstream of the second cryocooling phase 44 to generate a liquefied natural gas product 66. The liquefied natural gas 66 may then be transported to, for example, an offsite facility, customers, etc.

FIG. 3 represents a more specific embodiment of the hybrid refrigeration liquefaction system 20, which includes a series of cryocoolers that are heat integrated with the vapor compression refrigeration cycle 26. In the depicted embodiment, the flow path 22 leads the natural gas 24 to a first compressor 80, which is configured to increase the pressure of the natural gas 24 to generate a compressed natural gas 82. By way of non-limiting example, the first compressor 80 may increase the pressure of the natural gas 24 by between approximately 50% and 200%, such as between approximately 100% and 150%. As a specific example, the natural gas 24 may enter the system 20 at a pressure of between approximately 10 bar and 20 bar, between approximately 12 bar and 18 bar, or at approximately 14 bar. The first compressor 80 may increase the pressure of the natural gas 24 to between approximately 40 bar and 50 bar, such as approximately 42 bar and 48 bar, or approximately 46 bar.

The compressed natural gas 82 will generally have an increased temperature due to the heat of compression. Accordingly, it may be desirable to cool the compressed natural gas 82 before it is placed in heat exchange with the vapor compression refrigeration cycle 26 or the cryocooling phases, in order to enhance cooling efficiency. In the illustrated embodiment, the compressed natural gas 82 is provided along the flow path 22 to a first condenser 84 where the compressed natural gas 82 is cooled to generate a first cooled compressed natural gas 86. In one embodiment, the first cooled compressed natural gas 86 has a temperature of between 25° C. and 60° C., such as between about 30° C. and 50° C., upon exiting the first condenser 84.

The flow path 22 may then flow the first compressed natural gas 86 to the heat exchanger 30, which may represent a first heat exchanger in the illustrated embodiment. As discussed above, the heat exchanger 30 enables the transfer of thermal energy between the flow path 22 and the vapor compression refrigeration cycle 26. In the illustrated embodiment, the vapor compression refrigeration cycle 26 continuously circulates the refrigerant 32 through the heat exchanger 30 (i.e., the first heat exchanger 30). After exiting the heat exchanger 30, the refrigerant 32 will generally have a higher temperature than before provision thereto. The vapor compression refrigeration cycle 26 also includes equipment configured to suitably re-cool the refrigerant 32. As depicted, the cycle 26 includes a second compressor 88 that compresses the refrigerant 32, a second condenser 90 that condenses (at least partially) the refrigerant 32, and a throttling valve 92 or other similar expansion device that enables the refrigerant 32 to expand and cool. The vapor compression loop 28 also includes a series of heat exchangers 94 that enable heat integration between one or more of the cryocoolers of the system 20 and the vapor compression refrigeration cycle 26. The series of heat exchangers 94 are discussed in further detail below. However, in a general sense, the heat exchangers 94 may individually include any suitable heat exchanger capable of enabling the transfer of thermal energy between conduits, such as a shell and tube heat exchanger, plate heat exchanger, plate and shell heat exchanger, adiabatic wheel heat exchanger, plate fin heat exchanger, pillow plate heat exchanger, fluid heat exchanger, and the like.

In one embodiment, the natural gas 24, after cooling at the heat exchanger 30 by the refrigerant 32, may be a second cooled compressed natural gas 96 having a temperature of between 0° C. and −50° C., such as between approximately −10° C. and −40° C., or between approximately −30° C. and −40° C. In the illustrated embodiment, the second cooled compressed natural gas 96 (the pressure of which may be only slightly reduced compared to the first cooled natural gas 86) may be provided directly (e.g., with no intervening structures) to the first cryocooling phase 36, which includes first and second cryocoolers 98, 100 positioned in series along the flow path 22. In certain embodiments, the first and second cryocoolers 98, 100 may be thermoacoustic cryocoolers, or may be other types of cryocoolers.

The first cryocooler 98, as depicted, is in a heat exchange relationship with the refrigerant loop 28 of the vapor compression refrigeration cycle 26 via a second heat exchanger 102. This heat exchange relationship enable the first cryocooler 98 to expel its exhaust heat into a cool refrigerant stream as opposed to the ambient air, thereby allowing the first cryocooler 98 to operate more efficiently. By way of non-limiting example, the first cryocooler 98 may decrease the temperature of the natural gas to produce a third cooled compressed natural gas 104.

In one embodiment, the third cooled compressed natural gas 104 has a temperature between approximately −75° C. and −125° C. upon exiting the first cryocooler 104. After exiting the first cryocooler 98, the third cooled compressed natural gas 104 may flow along the flow path 22 toward the second cryocooler 100. A first expansion apparatus 106 may be positioned along the flow path 22 (or along a divergent flow path) between the first and second cryocoolers 98, 100. As noted above, such a device may enable overall increased cooling of the natural gas 24 and an increase in cooling efficiency by the cryocoolers. Indeed, as discussed in detail above, although the expansion caused by the expansion apparatuses disclosed herein may cause the amount of natural gas vapor to natural gas liquid to increase, the temperature of the natural gas 24 may be significantly decreased, which enables more efficient cooling in the cryocoolers. In certain embodiments, there may be more than one expansion apparatus, only one expansion apparatus, or no expansion apparatus between the first and second cryocoolers 98, 100.

The flow path 22 flows the third cooled compressed natural gas 104 (or an expanded and cooled natural gas, when the first expansion apparatus 106 is present) into the second thermoacoustic cryocooler 100, as noted above. The second thermoacoustic cryocooler 100 may also be in a heat exchange relationship with the refrigerant loop 28 of the vapor compression refrigeration cycle 26 via a third heat exchanger 108, which also enables the second cryocooler 100 to be continuously refreshed with a cooled medium, which increases efficiency. The second cryocooler 100 generates a fourth cooled natural gas 110, which may be a compressed or expanded fluid, depending on the presence of the first expansion apparatus 106. In embodiments where the first expansion apparatus 106 is not present between the first and second cryocoolers 90, 100, the fourth cooled natural gas 110 may have a temperature between −100° C. and −150° C., such as between −110° C. and −120° C. after exiting the second thermoacoustic cryocooler 100.

The flow path 22 may further include a second expansion apparatus 112, which operates to cause an expansion of the fourth cooled natural gas 110 to produce an expanded and cooled natural gas 114. By way of non-limiting example, the second expansion apparatus 112 may cause a pressure of the natural gas 24 to be decreased by between approximately 50% and approximately 10,000%, depending on the particular sizing of the second expansion apparatus 112. For instance, the pressure of the expanded and cooled natural gas 114 may be between approximately 1,000% and 5,000% less than, such as between approximately 2,000% and 5,000% less than, or between approximately 3,000% and 5,000% less than, the pressure of the fourth cooled natural gas 110. By way of example, the pressure of the fourth cooled natural gas 110 may be between approximately 30 bar and 60 bar, such as between approximately 40 bar and 50 bar, while the pressure of the expanded and cooled natural gas 114 may be between approximately 1 bar and 5 bar, such as between approximately 1.5 bar and 3 bar.

Again, this expansion causes a significant amount of cooling. For comparison, the natural gas 24 may only be cooled by another 10-15% at the second cryocooler 100 relative to the first cryocooler 98. However, the second expansion apparatus may cause the natural gas 24 to be cooled by another 30-40% relative to the second cryocooler 100. By way of non-limiting example, the expanded and cooled natural gas 114 may have a temperature between −140° C. and −175° C. after leaving the second expansion apparatus 112, such as between approximately −150° C. and −160° C. After the natural gas 24 is expanded and cooled at the second expansion apparatus 112, the natural gas 24 may be provided to the liquefied natural gas isolation system 42.

Again, the liquefied natural gas isolation system 42 includes the separation vessel 48, which includes the liquid and vapor outlets 58, 62, which flow the separated liquid and vapor phases 56, 60 of the natural gas 24, respectively, out of the separator 48. In the depicted embodiment, the vapor 60 flows to the at least one cryocooler 46 of the second cryocooling phase 44 for further cooling and condensation. The at least one cryocooler 46 may also be in a heat exchange relationship with the refrigerant loop 28 of the vapor compression refrigeration cycle 26 via a fourth heat exchanger 116, and will also obtain a similar benefit in terms of efficiency as described above for the first and second cryocoolers 98, 100.

In the at least one cryocooler 46 of the second cryocooling phase 44, substantially all of the vapor phase 60 of the natural gas 24 may be cooled and condensed to produce the second liquid stream 64. By “substantially all,” it is meant that at least 90% of the vapor phase 60 is condensed, such as between 90% and 100%, between 91% and 99%, or between 92% and 98%. The condensed vapor (as the second liquid 64) is then mixed with the first liquid 56 generated at the separator 48 in a mixer 120 to generate the product LNG 66.

It should be noted that various operational parameters of the hybrid refrigeration liquefaction system 20 may be monitored and affected/controlled, at least in part, using a control system 130, as illustrated in FIG. 4. The control system 130 may include any suitable type of control system, and may utilize and/or include one or more processing components 132, including microprocessors (e.g., field programmable gate arrays, digital signal processors, application specific instruction set processors, programmable logic devices, programmable logic controllers), tangible, non-transitory, machine-readable media 134 (e.g., memory such as non-volatile memory, random access memory (RAM), read-only memory (ROM), and so forth). The non-transitory machine-readable media 134 may collectively store one or more sets of instructions (e.g., algorithms) in computer-readable code form, and may be grouped into applications depending on the type of control performed by the control system 130. In this way, the control system 130 may be application-specific, or general purpose. Further, the control system 130 may include a series of distributed processor-based devices (e.g., as in a distributed control system), one or more workstations, or may be a centralized control system that is in communication with a series of devices configured to collect and relay feedback to the control system 130.

The control system 130 may be a closed loop control system (i.e., uses feedback to vary control parameters) or may be an open loop control system that does not use feedback for control. In the illustrated embodiment, the control system 130 is a closed loop system that collects feedback from a plurality of transducers disposed throughout the system 20, and, as a result of this feedback, may control the operation of various equipment to increase liquefaction efficiency and output a desired amount of the liquefied natural gas product 66 for export.

As depicted in the system 20 of FIG. 4 (in which certain features are not shown for clarity), the control system 130 may be communicatively coupled to a variety of machinery, in particular machinery that can be controlled using control signals. Such machinery may include the first and second compressors 80, 88 (in particular, the drivers of these compressors), one or more cryocooler drivers 136, and various other flow control devices that may be present in the system 20. Such flow control devices may include booster blowers/compressors and associated drivers, flow control valves and associated actuators, and the like. The feedback obtained by the control system 130 on which such control is at least partially based, is obtained using various signals generated by one or more sensors in the system 20, by power consumption of various pumps, drivers, and/or any other devices capable of being monitored. Various examples of such monitoring and control are provided herein.

By way of example, the sensors may include thermocouples configured to monitor a temperature of a given stream. The temperature sensors may generally be of the types K, E, T, N, J, B, S, R, or any combination thereof. In other embodiments, temperature may be monitored using other techniques, such as infrared monitoring techniques. The sensors may also include pressure transducers, pressure transmitters, gauges, and the like, for monitoring pressures, and orifice plate flow meters, venturi tube flow meters, flow nozzle flow meters, variable area or rotameter flow meters, or and the like, for monitoring flow. The terms “temperature sensor,” “pressure sensor,” and “flow sensor” are intended to encompass these examples.

By way of example, the control system 130 may obtain feedback indicative of a temperature and/or pressure of the natural gas 24 at various points along the flow path 22 upstream of the first cryocooling phase 36 using one or more first pressure sensors 138 and/or one or more first temperature sensors 140. The flow of the natural gas 24 along the flow path 22 upstream of the first cryocooling phase 36 may also be monitored using one or more first flow sensors 142. It should be noted that the sensors 138, 140, 142 may be positioned at any point along the flow path 24, such as at points that provide a suitable indication of how a variation in an operational parameter of a given piece of equipment changes the attributes of the natural gas 24 within the flow path 22.

By way of example, the pressure and/or temperature and/or flow monitored using these sensors 138, 140, 142 may provide an input to an algorithm performed by the control system 130 to control the first compressor 80 (e.g., a speed of the first compressor), which will generally affect the flow, pressure, and temperature of the natural gas 24. The control system 130 may also use these inputs to control a flow of a cooling medium that is used within the condenser 84 to control the amount of thermal energy withdrawn from the incoming pressurized stream.

Similarly, the temperature, flow, and pressure of the refrigerant 32 within the vapor compression refrigeration cycle 26 may be monitored using one or more second temperature sensors 144, one or more second flow sensors 146, and one or more second pressure sensors 148. As a result of this monitoring, the control system 130 may control a speed of the second compressor 88 and, in certain embodiments, the flow of a cooling medium provided to various condensers of the cycle 26.

The temperature, pressure, and flow of the natural gas 24 through the first cryocooling stage 36 may be similarly monitored using one or more third temperature, pressure, and flow sensors 150. By way of example, these parameters may be used individually or in any combination to control the operation of the one or more cryocooler drivers 136 (e.g., a speed of the cryocooler drivers 136). Further, in embodiments where the first cryocooling phase 36 includes one or more expansion apparatuses having a variable opening or orifice size, the control system 130 may adjust the orifice size as appropriate.

In certain embodiments, the hybrid liquefaction system 20 may include other types of intermediate cooling phases, such as one or more magnetic refrigeration phases 152. The illustrated magnetic refrigeration phase 152 (or the residence time of the natural gas 24 in the magnetic refrigeration phase 152) may be at least partially controlled by the control system 130 based at least partially on pressure, temperature, and/or flow information relating to the natural gas 24 exiting the first cryocooling phase 36. Additionally or alternatively, the operation of the magnetic refrigeration phase 154, or the residence time of the natural gas 24 therein, may be at least partially based on the monitored temperature, pressure, and/or flow of the natural gas 24 within the magnetic refrigeration phase 152 as measured by one or more fourth temperature, pressure, and flow sensors 154.

It should be noted that temperature, pressure, and flow sensors may also be positioned anywhere throughout the liquefied natural gas isolation system 42. For example a temperature, pressure, and/or flow of the vapor stream 60 and/or the liquid stream 56 exiting the separator 48 may be inputs to control algorithms performed by the control system 130 for controlling the separator 48 (e.g., a pressure within the separator 48).

The second cryocooling phase 44 may also be similarly monitored and controlled. Indeed, control algorithms performed by the control system 130 may use temperature, pressure, and/or flow data provided by one or more fifth temperature, pressure, and/or flow sensors 156 positioned upstream, downstream, and/or within the second cryocooling phase 44.

As noted above, the present inventors have found that significant increases in cooling efficiency may be obtained when one or more expansion devices are used in combination with the cryocoolers, and when a single driver is used to power at least two cryocoolers. FIGS. 5 and 6 schematically depict simplified process flow diagrams of such approaches, and, more specifically, different embodiments of the manner in which at least two cryocoolers may be driven using the same driver. Specifically, FIG. 5 depicts a simplified schematic of the system 20, where multiple cryocoolers are arranged in parallel in order to increase the throughput of the system 20. Indeed, in accordance with the depicted approach, the system 20 may be capable of generating at least about 5,000 gallons (e.g., 18,900 liters) of liquefied natural gas per day, such as between 5,000 gallons and 15,000 gallons (e.g., 57,000 liters) of liquefied natural gas per day (e.g., approximately 10,000 gallons per day, about 38,000 liters per day), depending on the number of cryocoolers employed.

In the embodiment depicted in FIG. 5, the flow path 22 splits into a plurality of intermediate flow paths 168, each intermediate flow path 168 flowing a portion of the natural gas 24 through two or more cryocoolers and other cooling features. In the illustrated example, the parallel intermediate flow paths 168 include a plurality of first cryocoolers 170, which may generally correspond to the first cryocooling phase 36, a plurality of second cryocoolers 172, which may generally correspond to the second cryocooling phase 44 (but may, alternatively, be a part of the first cryocooling phase 36), and a plurality of expanders 174 positioned along the flow path 22 between each pair of the first and second cryocoolers 170, 172, which are arranged in a series configuration 176.

Again, the series arrangement of the cryocoolers 170, 172 in combination with the expander 174 disposed therebetween may exhibit enhanced cooling efficiency compared to embodiments where no expander is employed between the cryocoolers. The system 20, as depicted, includes a plurality of these series configurations 176 arranged in parallel. While the illustrated embodiment is depicted as including 5 such series configurations 176, any number of series configurations 176 may be used, depending on the limitations of the flow path 22, the compressor 80, and the vapor compression refrigeration cycle 26. By way of example, there may be between 2 and 20, 4 and 12, or 6 and 10 series configurations 176 arranged in parallel.

As depicted in the expanded view, each series configuration 176 further includes a single driver 180, which may be matched to the power requirements of each cryocooler. In the illustrated embodiment and by way of example only, the driver 180 may be a 4×10 kW driver that produces 40 kW total power. Other such drivers that may be used include a 2×20 kW driver that similarly produces 40 kW total power, where each cryocooler has a 40 kW requirement. Indeed, any appropriate driver may be selected based on the power requirements of the cryocoolers, and is considered to be within the scope of the present disclosure. In accordance with present embodiments, the use of the single driver 180, as noted above, may enhance the efficiency of the system 20 by enabling the driver to operate one cryocooler using parasitic losses incurred by the other cryocooler, which would otherwise be wasted.

The cryocoolers 170, 172 may be commonly driven and overall losses reduced using a common buffer tube 182 and a common compliance tank 184. However, embodiments where each cryocooler 170, 172 utilizes its own buffer tube and compliance tank are also within the scope of the present disclosure. Additionally, embodiments where each driver only drives a single cryocooler are also within the present scope. Indeed, any combination of drivers driving one cryocooler or more than one cryocooler, and any combination of the use of common buffer tubes and compliance tanks is presently contemplated. In other words, the present disclosure encompasses embodiments where any one or a combination of the series configurations 176 use a single driver or multiple drivers, a single buffer tube or multiple buffer tubes, and a single compliance tank or multiple compliance tanks.

In addition to, or as an alternative to, driving multiple (i.e., two or more) cryocoolers in series using a single driver, in some embodiments, a single driver may be used to drive cryocoolers that are positioned in parallel, such as two or more of the first cryocoolers 170 and/or two or more of the second cryocoolers 172. Such an embodiment is depicted in FIG. 6. It should be noted that the approaches described above with respect to FIG. 5, including driving cryocoolers in series, may be used in any suitable combination with the approaches described with respect to FIG. 6. In other words, in certain embodiments, a single driver may drive two or more cryocoolers in series, while another single driver may drive two or more separate cryocoolers in parallel.

In the embodiment illustrated in FIG. 6, the system 20 includes a similar arrangement to that shown in FIG. 5, where the flow path diverges into a plurality of intermediate paths 168, each path having one of the first cryocoolers 170 positioned upstream of one of the second cryocoolers 174 along its respective intermediate flow path 168. In addition, one or more of the expansion apparatuses 174 may be positioned along the intermediate flow paths 168. Furthermore, it should be noted that while the intermediate flow paths 168 may flow through generally the same arrangement of features to facilitate design and control, that embodiments where certain of the intermediate flow paths 168 flow through a different arrangement of features (e.g., a different number of cryocoolers, expanders, blowers, flow control devices) are also within the scope of the present disclosure.

The expanded view of FIG. 6 depicts a parallel configuration 190 in which two of the first cryocoolers, 170A and 170B, arranged in parallel intermediate flow paths 168A and 168B, respectively, are driven by a single driver 192. Again, the single driver 192 may be matched to the power requirements of each of the cryocoolers. In the illustrated embodiment and by way of example only, the single driver 192 of FIG. 6 may be a 2×20 kW driver that produces 40 kW total power. Other such drivers that may be used include, but are not limited to, a 4×10 kW driver that similarly produces 40 kW total power, where each cryocooler has a 40 kW requirement. Again, the driver 192 may be matched to the power requirements of the cryocoolers such that a plurality of cryocoolers having a particular power requirement, denoted as “N,” may be driven by a single driver designated as an M×N/M driver.

As with the series arrangements 176 where the cryocoolers 170, 172 are commonly driven, and overall losses may be further reduced using a common buffer tube 194 and a common compliance tank 196 in combination with the single driver 192 for the first cryocoolers 170A and 170B. It should be noted that there may be one, or more than one such parallel driving arrangement 190 in the system 20. Indeed, the number of parallel driving arrangements 190 may be less than or equal to the number of exclusive sets of cryocoolers in the system 20 (i.e., sets of cryocoolers that when commonly driven, can no longer be considered to be a part of another set). Each set may include two or more cryocoolers.

In addition, embodiments where each cryocooler 170A, 170B utilizes its own buffer tube and compliance tank are also within the scope of the present disclosure. Further, any combination of drivers driving one cryocooler or more than one cryocooler (in series and/or in parallel), and any combination of the use of common buffer tubes and compliance tanks, is presently contemplated. Thus, the present disclosure encompasses embodiments where any one or a combination of the series configurations 176 and/or the parallel configurations 190 use a single driver or multiple drivers, a single buffer tube or multiple buffer tubes, and a single compliance tank or multiple compliance tanks.

FIG. 7 is a block diagram of an embodiment of a method 210 of natural gas liquefaction utilizing a hybrid refrigeration scheme. It should be noted that while the embodiments disclosed above enable performance of the method 210, other specific arrangements are possible and are considered to be within the scope of the present disclosure to the extent that the other arrangements are able to perform the acts disclosed herein. Indeed, the inventors have found that the performance of the particular acts disclosed herein may significantly enhance the efficiency of cryocooling of natural gas, as well as enable the liquefaction of natural gas on an industrial scale using cryocoolers.

In the illustrated embodiment, the method 210 includes cooling (block 212) a natural gas feed with a vapor compression refrigeration cycle. The acts represented by block 212 may include cooling the natural gas feed with a single vapor compression refrigeration cycle or multiple such cycles. The cycles may be the same, but do not necessarily have the same configuration and may be different (e.g., use different refrigerants) based on the particular heat capacity of the refrigerant and the temperature of the incoming natural gas feed.

The method 210 may further include cooling (bock 214) the natural gas feed with at least one cryocooler, such as between 1 and 20 cryocoolers arranged in series, parallel, or any combination thereof. The cryocoolers may be the same type (e.g., thermoacoustic) or any combination of different types (e.g., Joule-Thomson cooler, Gifford-McMahon cooler, Stirling cooler, pulse tube refrigerator, adiabatic demagnetization refrigerator). Furthermore, when there are multiple cryocoolers, at least two of the cryocoolers may be driven by a single driver/drive unit to enhance efficiency.

In one embodiment, the acts represented by block 212 may be performed before the acts of block 214, for example when the vapor compression refrigeration cycle is upstream from a cryogenic cooling phase that has the at least one cryocooler. In an alternative embodiment, however, the acts represented by block 214 may be performed before the acts represented by block 212, for instance when the vapor compression refrigeration cycle is downstream from the cryogenic cooling phase. As discussed above, it may be advantageous to cool the natural gas first using the vapor compression refrigeration cycle before cooling the natural gas using the cryocooler. Thus, it may be desirable to perform the acts represented by block 212 before the acts represented by block 214. However, either order is presently contemplated.

Before, during, or after cooling using the at least one cryocooler in accordance with the acts of block 214, the natural gas may undergo expansion using, for example, an expansion device such as a Joule-Thomson valve. The expansion in accordance with block 214 may cause the natural gas 24 to cool via isentropic expansion, such that even though a substantial portion of the natural gas 24 is in the vapor phase, the overall combination of the liquid and vapor phases is at a much lower temperature compared to the temperature of the natural gas 24 before expansion. By way of example, the natural gas 24 may be cooled by between approximately 10% and approximately 50%, depending on the particular configuration of the expander.

The natural gas 24, after expansion, and even after some additional cooling by one or more cryocoolers, may contain a vapor portion that constitutes between 1% and 50% of the natural gas stream. To ensure that the vapor portion is properly cooled, the method 210 also includes separating (block 218) the vapor and liquid phases from one another, for example using a separator. The separator may be a flash tank or other distillation-type vessel held at a pressure sufficient to effect the separation of the constituent phases.

The liquid portion is then collected (block 220) or otherwise continues to flow as a liquid, while the vapor portion undergoes further cooling (block 222). As an example, the further cooling may be performed using one or more additional cryocoolers of any suitable type. In addition, in certain embodiments, the cryocoolers used for cooling in accordance with block 222 may be driven by a driver/drive unit that also drives at least one other cryocooler that performs at least part of the cooling in accordance with block 214. The additional cooling will generally condense substantially all of the vapor into a liquid phase to generate a second portion of liquefied natural gas.

After the first and second portions of liquefied natural gas are generated, the method 210 includes combining (block 224) the two portions to generate a liquefied natural gas product. The liquefied natural gas product may be stored in a suitable vessel (e.g., a pressurized and/or cryogenic container), or provided to one or more offsite facilities as a liquid flow.

FIG. 8 depicts an embodiment of a method 230 in which the natural gas 24, flowing along path 22, may be utilized as a refrigerant in one or more refrigeration loops. It should be noted that the method 230 may be used alone or in combination with any of the other embodiments disclosed herein. A system configured to perform the acts of method 230 is described in further detail below with respect to FIG. 9.

The method 230 may begin, or include, compressing and cooling (block 232) the feed natural gas 24, for example in one or more first heat exchangers with a recycle vapor (e.g., a vapor generated from the natural gas 24 itself). The recycle vapor may be generated from the natural gas 24 by, for example, separating the natural gas 24 (e.g., after the acts of block 232) into a first portion and a second portion at a first heat exchanger, where the first portion and the second portion are subjected to different pathways and may have different end uses.

By way of example, the first portion of the natural gas 24 may be recompressed (block 236), i.e., compressed again, and utilized for cooling within the refrigeration loop 26. For example, the first portion of the natural gas 24 may be utilized as at least one refrigerant within the refrigeration loop 26, where the first portion 24 is compressed, cooled, and expanded.

Once expanded, the first portion of the natural gas 24 may be placed into a heat exchange relationship with the second portion of the natural gas 24. In this respect, the method 230 includes further cooling and condensing (block 238) the second portion of the natural gas 24, for example in a second heat exchanger downstream from the first heat exchanger.

Once the acts in accordance with block 238 are performed, the method 230 may include expanding (block 240) the second portion of the natural gas 24 to transform it from a liquid at a first pressure to a liquid/vapor mixture at a second pressure, the second pressure being lower than the first pressure. The acts of block 240 may be performed by any suitable expanding device, such as a Joule-Thomson valve. It may be desirable to expand the natural gas in this manner to enable the eventual production of liquefied natural gas at a lower pressure than would be otherwise achieved.

Once the liquid/vapor natural gas mixture is generated, it may be subjected to further cooling (block 242) using a cryocooling phase. The cryocooling phase may include one or more cryocoolers (e.g., thermoacoustic cryocoolers) configured to condense the vapor portion of the liquid/vapor natural gas mixture. In one embodiment, the liquid/vapor natural gas mixture may be subjected to a separator (e.g., separator 48 of FIGS. 2-4), where the liquid and vapor portions of the natural gas are allowed to separate based at least on pressure, and the vapor portion may be condensed. The condensed vapor (i.e., liquid) natural gas from the cryocooling phase may then be combined with the liquid portion generated at the separator to produce the liquefied natural gas product, for example a low pressure natural gas product.

FIG. 9 depicts an embodiment of the hybrid refrigeration liquefaction system 20, which is configured to perform the acts of method 230. It should be noted, however, that the system 20 of FIG. 9 may include features that may be used in any combination with any one or more of the embodiments described above with respect to FIGS. 2-7.

As illustrated, the hybrid refrigeration liquefaction system 20 includes the flow path 22, which receives the natural gas 24 and flows the natural gas 24 through a first heat exchanger 250 and a second heat exchanger 252, which are both in a heat exchange relationship with one or more vapor compression refrigeration cycles 26. In the illustrated embodiment, the first and second heat exchangers 250, 252 are in a heat exchange relationship with a single vapor compression refrigeration cycle 26. The natural gas is subsequently cooled in at least one cryocooling phase (e.g., first and second cryocooling phases 36, 44).

In addition, at least a portion of the natural gas 24 is utilized as a refrigerant in the refrigerant loop 28 of the vapor compression refrigeration cycle 26. In the illustrated embodiment, the first heat exchanger 250 enables the incoming compressed natural gas stream to be cooled. A stream of compressed and cooled natural gas 254 may exit the first heat exchanger 250 (e.g., as a bottoms discharge) into the refrigeration loop 28. The loop 28 may flow the stream of compressed and cooled natural gas 254 to the second compressor 88 for further compression, to the heat exchanger 90 for additional cooling. A resulting stream of re-compressed and cooled natural gas 256 may then be divided into a first portion 258 and a second portion 260, for example by diverting the first portion 258 into a divergent pathway 262 extending from the refrigerant loop 28.

The divergent pathway 262 may carry the first portion 258 back into a heat exchange relationship (e.g., direct or indirect) with the natural gas flow path 22 (e.g., between the first and second heat exchangers 250, 252) to generate natural gas liquids (NGL's) 264. The NGL's 264 may include, among others, small-chain hydrocarbons such as ethane, propane, butane, and the like.

The second portion 260 may continue along the refrigerant loop 28 and to the expander 92, where the second portion 260 becomes a refrigerant natural gas 266 having a pressure and temperature suitable for cooling the natural gas 24 within the second heat exchanger 252. In other words, the refrigerant natural gas 266 may be at a lower temperature than an incoming stream of natural gas 268 generated at the first heat exchanger 250. In this regard, the first and second heat exchangers 250, 252 are positioned in heat exchange with the refrigerant loop 28 in such a way so as to enable the natural gas 24 flowing therethrough to have its lowest temperature when it undergoes heat exchange at the second heat exchanger 252.

The natural gas, having been further cooled within the second heat exchanger 252, may then flow along the flow path 22 and to the one or more expansion apparatuses 40, the separator 48, and one or more cryocooling phases 36, 44 as described above with respect to any of the embodiments of FIGS. 2-6. In accordance with one embodiment, the product LNG 66 may be at a lower pressure compared to liquefaction using compression and refrigeration techniques alone (e.g., without the use of additional expansion between the vapor compression refrigeration cooling phase and the one or more cryocooling phases).

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

1. A gas feed liquefaction system, comprising: a flow path; an initial cooling phase in a first heat exchange relationship with the flow path, wherein the initial cooling phase comprises a vapor compression refrigeration cycle; a second cooling phase in a second heat exchange relationship with the flow path, wherein the second cooling phase comprises a first cryocooler in series with the initial cooling phase; and a first expander positioned along the flow path between the first cryocooler and a separation vessel comprising a first liquid outlet and a vapor outlet.
 2. The system of claim 1, comprising a first heat exchanger placing the flow path and the initial cooling phase in the first heat exchange relationship, and a second heat exchanger heat-integrating the initial cooling phase and the first cryocooler or an additional cryocooler of the gas feed liquefaction system.
 3. The system of claim 1, comprising a third cooling phase having a second cryocooler positioned downstream of the vapor outlet of the separation vessel, wherein the first and second cryocoolers are driven using a single driver.
 4. The system of claim 3, comprising a liquid product outlet path, wherein the liquid product outlet path comprises a mixer comprising first and second inlets in fluid communication with the first liquid outlet of the separation vessel and a second liquid outlet of the second cryocooler.
 5. The system of claim 3, wherein the first and second cryocoolers share a common buffer tube and a common compliance tank.
 6. The system of claim 1, wherein the second cooling phase comprises a second cryocooler positioned along the flow path between the first cryocooler and the separation vessel, wherein the first expander is positioned between the first and second cryocoolers, or between the second cryocooler and the separation vessel.
 7. The system of claim 6, comprising a driver configured to power the first and second cryocoolers, wherein the first and second cryocoolers are connected via a common buffer tube.
 8. The system of claim 1, wherein the flow path splits into a plurality of intermediate flow paths arranged in a parallel relationship, the first cryocooler is positioned along a first one of the intermediate flow paths, the second cooling phase comprises a second cryocooler positioned along a second one of the intermediate flow paths, and the first and second cryocoolers are driven by a common driver, are connected by a common buffer tube, and the first and second cryocoolers both use the same compliance tank.
 9. The system of claim 8, comprising: a third cryocooler positioned along the first one of the intermediate flow paths in series with the first cryocooler, wherein the first expander is positioned along the first one of the intermediate flow paths between the first and third cryocoolers; a fourth cryocooler positioned along the second one of the intermediate flow paths in series with the second cryocooler; and a second expander positioned along the second one of the intermediate flow paths between the second and fourth cryocoolers.
 10. The system of claim 1, wherein at least one of the heat exchangers within the vapor compression refrigeration cycle places the refrigeration loop of the vapor compression refrigeration cycle in the first heat exchange relationship with a working fluid in at least one of the first and second thermoacoustic cryocoolers.
 11. The system of claim 1, wherein the initial cooling phase is downstream from a natural gas processing facility or gasification plant.
 12. A system comprising: a natural gas flow path; a vapor compression refrigeration cycle configured to remove heat from the natural gas flow path; a first cryogenic cooling phase comprising at least two cryocoolers configured to remove heat from the natural gas flow path; a driver configured to drive the at least two cryocoolers, wherein the at least two cryocoolers are connected by a common buffer tube; and a liquefied natural gas outlet path downstream from the vapor compression refrigeration cycle and the cryogenic cooling phase.
 13. The system of claim 12, comprising a separation vessel positioned along the natural gas flow path and having a natural gas vapor outlet and a liquefied natural gas outlet leading to the liquefied natural gas outlet path, wherein at least a portion of a second cryogenic cooling phase is positioned in fluid communication with the natural gas vapor outlet to enable the second cryogenic cooling phase to condense natural gas exiting the natural gas vapor outlet of the separation vessel.
 14. The system of claim 12, wherein at least one of heat exchanger within the vapor compression refrigeration cycle places a refrigeration loop of the vapor compression refrigeration cycle in a heat exchange relationship with a working fluid of a first cryocooler of the at least two cryocoolers.
 15. The system of claim 12, comprising an expander positioned between the at least two cryocoolers that causes natural gas to expand and cool.
 16. The system of claim 12, comprising an expander positioned between the at least two cryocoolers and the liquefied natural gas outlet path.
 17. A method comprising: cooling a fluid along a fluid path using a vapor compression refrigeration cycle; cooling the fluid along the fluid path using at least one cryocooler of a cryogenic cooling phase; expanding the fluid during cooling within the cryogenic cooling phase, after cooling in the cryogenic cooling phase, or a combination thereof, such that a temperature and pressure of the fluid are reduced to generate a fluid stream having both a vapor phase and a liquid phase; and condensing the vapor phase.
 18. The method of claim 17, comprising separating the vapor phase and liquid phase from one another before condensing the vapor phase.
 19. The method of claim 18, comprising condensing the vapor phase using an additional cryogenic cooling phase.
 20. The method of claim 19, wherein the cryogenic cooling phase comprises first and second cryocoolers that are driven using the same driver, wherein the first and second cryocoolers are connected by a common buffer tube.
 21. The method of claim 17, wherein the fluid is natural gas.
 22. The method of claim 17, comprising cooling a working fluid of the cryogenic cooling phase using the vapor compression refrigeration cycle. 